EC 2.5.1.69     
Accepted name: lavandulyl diphosphate synthase
Reaction: 2 prenyl diphosphate = diphosphate + lavandulyl diphosphate
Glossary: lavandulyl = 5-methyl-2-(prop-1-en-2-yl)hex-4-en-1-yl
Other name(s): FDS-5; dimethylallyl-diphosphate:dimethylallyl-diphosphate dimethylallyltransferase (lavandulyl-diphosphate-forming)
Systematic name: prenyl-diphosphate:prenyl-diphosphate prenyltransferase (lavandulyl-diphosphate-forming)
Comments: Lavandulyl diphosphate is a monoterpene with a non-head-to-tail linkage. It is unlike most monoterpenoids, which are derived from geranyl diphosphate and have isoprene units that are linked head-to-tail. When this enzyme is incubated with prenyl diphosphate and 3-methylbut-3-en-1-yl diphosphate, it also forms the regular monoterpene geranyl diphosphate [2]. The enzyme from Artemisia tridentata (big sagebrush) forms both lavandulyl diphosphate and chrysanthemyl diphosphate (see EC 2.5.1.67, chrysanthemyl diphosphate synthase) when prenyl diphosphate is the sole substrate.
References:
1.  Erickson, H.K. and Poulter, C.D. Chrysanthemyl diphosphate synthase. The relationship among chain elongation, branching, and cyclopropanation reactions in the isoprenoid biosynthetic pathway. J. Am. Chem. Soc. 125 (2003) 6886–6888. [PMID: 12783539]
2.  Hemmerlin, A., Rivera, S.B., Erickson, H.K. and Poulter, C.D. Enzymes encoded by the farnesyl diphosphate synthase gene family in the Big Sagebrush Artemisia tridentata ssp. spiciformis. J. Biol. Chem. 278 (2003) 32132–32140. [PMID: 12782626]
[EC 2.5.1.69 created 2007]